This invention relates to a transducer motor having a rotor comprising a permanent dipole magnet and a stator comprising coils wound in a particular fashion to interact with the magnet.
Several proposals have been made to use rotary motors to drive the radiator of a transducer or loudspeaker. This is in contrast to conventional loudspeakers having linear drives, in which a cylindrical voice coil is suspended around its axis between the poles of a magnet and is axially movable along the axis to a limited extent.
In U.S. Pat. No. 4,763,358, the rotary shaft of a motor is connected directly to a vane and enclosed within a baffled enclosure. The motor employed is of the commutated type, in which the current in the coil of the rotor is switched to the active portion of the coil as it rotates. As a result, the force per unit current on the shaft remains constant, irrespective of the rotary position or degree of rotation of the shaft.
Another loudspeaker driven by a motor is described in U.S. Pat. No. 4,564,727. In this patent, the rotary motion of the shaft of a commutated motor is converted to linear motion and is used to drive the radiator of the speaker.
The use of rotary motors to drive loudspeakers offers numerous improvement over conventional drives. Rotary motors are generally more efficient, may have an unlimited degree of movement, and, with commutation, can provide a constant force per unit of current. Linear drives of conventional voice coil speakers are limited by the mass of the moving coil, limited excursion, maximum available magnet strength, and the like. On the other hand, conventional commutated rotary motors are relatively complicated in design and expensive to produce, and also may have limited velocity and acceleration values.